Increasing use of mobile telecommunications in business life has substantial advantages because of its convenience. One of the risks is, however, unauthorized interception, such as eavesdropping or the unauthorized reception of telephone calls and data transmission. Eavesdropping is the use of a mobile device, such as a smartphone, as a listening device to overhear a conversation.
A number of methods and devices have been developed in order to overcome this unauthorized interception. For example, it is possible to sweep regularly rooms or buildings for listening devices, which may have been installed in the rooms and/or on the communication networks to the rooms or building. It is possible to construct one or more rooms in a building with a Faraday cage to prevent electromagnetic waves from entering or exiting the room or the building. It is also possible to generate random noise over a wide variety of radio frequencies to block any transmission or reception of any mobile devices/stations, such as smartphones or mobile telephones within a particular area.
These prior art methods have a number of issues associated with them. For example, the construction of a Faraday cage within a building is extremely expensive and is not practical in many cases. Regular sweeping of buildings for listening devices can be costly and is never 100% effective. Blanket jamming of all radio frequencies can also lead to interference of acceptable communication devices and also conflict with other users of telecommunication networks. It would therefore be desirable to develop a system, based on existing mobile telecommunication systems, which blocks telecommunications calls in a limited coverage area and within a defined time frame, thus preventing substantially eavesdropping or other unauthorized interception.
A smart signal jammer is, for example, known from U.S. Pat. No. 7,982,654 B2 which discloses the transmission of one or more jamming signals in one or more temporal transmission patterns of pulses and is able to jam any unwanted signals in its range. One or more of the smart signal jammers of this patent must be distributed throughout the building in order to ensure that all of the signals in the building are sufficiently jammed. The installation of a number of the signal jammers can be expensive and can also disturb telecommunication signals outside of the building, which will disrupt calls and data transmission of ‘normal’ users.
This issue of disturbing the telecommunication signals for other users outside of the intended range of the jamming signals in which the telecommunication signals are to be blocked is serious, as it can lead to a number of complaints to the telecommunication operators. There is therefore a need to reduce this disturbance as much as possible.
The distributed antenna system of this disclosure can be used to secure business, military or government meeting rooms from eavesdropping. The distributed antenna system could also be permanently installed in prisons or trading rooms in which no communication through mobile stations is allowed.